Method of determining position on a magnetic track of an encoder

ABSTRACT

A method of determining a position on a magnetic track of an encoder includes providing a group of magnetic pole pairs that forms a portion of the magnetic track, recording a relative position within a first magnetic pole pair in the group using a first magnetic sensor proximate a high-resolution portion of the magnetic track, detecting adjacent pole junctions within the group of magnetic pole pairs with a second magnetic sensor positioned proximate a reference portion of the magnetic track, correlating the adjacent pole junctions with the first magnetic pole pair to determine a relative position of the first magnetic pole pair within the group, and calculating a local absolute position within the group using the relative position within the first magnetic pole pair and the relative position of the first magnetic pole pair within the group.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 13/259,252 filed on Sep. 23, 2011, now U.S. Pat. No. 8,823,365, which is a national stage entry under 35 U.S.C. §371 of InternationalPatent Application No. PCT/US2010/029729 filed on Apr. 2, 2010, whichclaims priority to U.S. Provisional Patent Application No. 61/166,946filed on Apr. 6, 2009, the entire contents of all of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to sensor assemblies, and moreparticularly to magnetic encoders including a magnetic track with aplurality of magnetic pole pairs.

BACKGROUND OF THE INVENTION

Magnetic encoders are typically utilized to determine a position of amoving object in a mechanical system so the position or movement of theobject can be controlled in the mechanical system. Magnetic encoderstypically include a target, including dual multi-pole magnetic tracks,mounted on the moving object and magnetic sensors (e.g., strings ofHall-effect devices) placed in proximity to the poles of the respectivemagnetic tracks. The pole spacing of the respective magnetic tracks istypically different to induce a phase difference in the signals detectedby the magnetic sensors over the respective tracks. The phase differencebetween the respective signals of the magnetic sensors is then utilizedto determine the position of the target, and therefore the movableobject, at any given time. In other words, the position of one of themagnetic tracks (i.e., the “measured track”) can be determined bycomparing the signal output by the magnetic sensor over the measuredtrack and the signal output by the magnetic sensor over the other track(i.e., the “reference track”).

SUMMARY OF THE INVENTION

The present invention provides, in one aspect, a method of determining aposition on a magnetic track of an encoder. The method includesproviding a group of magnetic pole pairs that forms a portion of themagnetic track, recording a relative position within a first magneticpole pair in the group using a first magnetic sensor proximate ahigh-resolution portion of the magnetic track, detecting adjacent polejunctions within the group of magnetic pole pairs with a second magneticsensor positioned proximate a reference portion of the magnetic track,correlating the adjacent pole junctions with the first magnetic polepair to determine a relative position of the first magnetic pole pairwithin the group, and calculating a local absolute position within thegroup using the relative position within the first magnetic pole pairand the relative position of the first magnetic pole pair within thegroup.

Other features and aspects of the invention will become apparent byconsideration of the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a first embodiment of a sensor assembly ofthe present invention, illustrating a magnetic track and two magneticsensors disposed proximate a first location on the magnetic track.

FIG. 2 is a schematic view of a single microchip incorporating the twomagnetic sensors of FIG. 1.

FIG. 3 is a schematic view of the magnetic sensors of FIG. 1 disposedproximate a second location on the magnetic track.

FIG. 4 is a schematic view of a conventional sensor assembly operable tooutput U, V, W style commutation signals.

FIG. 5 is a graph illustrating U, V, W style commutation signals thatmay be output by the conventional sensor assembly of FIG. 4 or themagnetic encoder of FIG. 1.

FIG. 6 is a schematic view of another embodiment of a sensor assembly ofthe present invention.

FIG. 7 is a schematic view of yet another embodiment of a sensorassembly of the present invention, illustrating a magnetic track and twomagnetic sensors disposed proximate a first location on the magnetictrack.

FIG. 8 is a schematic view of the magnetic sensors of FIG. 7 disposedproximate a second location on the magnetic track.

FIG. 9 is a schematic view of another embodiment of a sensor assembly ofthe present invention, illustrating pole junctions having differentoffset dimensions.

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting.

DETAILED DESCRIPTION

With reference to FIG. 1, a sensor assembly or a magnetic encoder 10 isschematically illustrated. The encoder 10 includes a magnetic track 14having a plurality of North/South pole pairs 18. Although the magnetictrack 14 is schematically illustrated in a linear configuration forclarity, the encoder 10 is configured as a rotary encoder including arotating target 22 upon which the magnetic track 14 is mounted. In sucha configuration, the magnetic track 14 would be circular and concentricwith the rotational axis of the rotating target 22. However, the encoder10 of the present invention may alternatively be configured as a linearencoder, incorporating substantially similar structure and a method ofoperation as described herein with respect to the rotary encoder 10.

With continued reference to FIG. 1, only a portion of the magnetic track14 is shown. Specifically, the illustrated portion of the magnetic track14 includes a group 26 of four pole pairs 18 a-18 d, each of whichincludes a pole junction 30 separating the individual North/South polesin the respective pole pairs 18. Each of the pole junctions 30 isdivided into a high-resolution segment 34 corresponding with ahigh-resolution portion 38 of the magnetic track 14, and a referencesegment 42 a, 42 b corresponding with a reference portion 46 of themagnetic track 14 (discussed in more detail below). Each of the polejunctions 30 in the magnetic track 14 is also jogged or stepped, suchthat the reference segment 42 a, 42 b of each of the pole junctions 30is offset from the high-resolution segment 34 of the same pole junction30. More particularly, the high-resolution segments 34 of adjacent polejunctions 30 are equally spaced from each other, while the referencesegments 42 a, 42 b of adjacent pole junctions 30 may be unequallyspaced, depending upon the direction of offset of the adjacent referencesegments 42 a, 42 b.

With continued reference to FIG. 1, some of the pole junctions 30include a reference segment 42 a that is offset to the right of thehigh-resolution segment 34 of the same pole junction 30 (i.e., aright-offset reference segment 42 a), while other pole junctions 30include a reference segment 42 b that is offset to the left of thehigh-resolution segment 34 of the same pole junction 30 (i.e., aleft-offset reference segment 42 b). The reference segments 42 a, 42 bmay be arranged within the group 26 of adjacent magnetic pole pairs 18a-18 d to provide a unique combination or sequence of states (e.g.,either right-offset or left-offset) for each pole pair 18 a-18 d in thegroup 26. As a result, a particular pole pair 18 a-18 d may beidentified by matching it with its associated unique combination ofadjacent right-offset and left-offset reference segments 42 a, 42 b.Using this “two-state” logic (i.e., using only right-offset andleft-offset reference segments 42 a, 42 b), the four adjacent pole pairs18 a-18 d illustrated in FIG. 1 can be uniquely identified according toTable 1 below, in which “R” denotes a right-offset reference segment 42a and “L” denotes a left-offset reference segment 42 b.

TABLE 1 Pole Pairs Pole Junctions 1 2 3 4 North/South L L R RSouth/North L R L RThe North/South pole junction is the pole junction 30 between the Northand South poles within a particular pole pair 18 a-18 d, while theSouth/North pole junction is the pole junction 30 between the South poleand the North pole of adjacent pole pairs 18 a-18 d. As described inmore detail below, the magnetic encoder 10 of the present invention isoperable to determine the absolute position of the magnetic track 14locally within the group 26 of four magnetic pole pairs 18 a-18 d byrecognizing the unique combination of adjacent right-offset andleft-offset reference segments 42 a, 42 b separating the individualpoles in the pole pairs 18 a-18 d.

The magnetic encoder 10 also includes a first or high-resolutionmagnetic sensor 50 proximate the high-resolution portion 38 of the track14, and a second magnetic sensor 54 proximate the reference portion 46of the track 14. Each of the sensors 50, 54 is configured as a Hallstring multiplying sensor, and both sensors 50, 54 are disposed on asingle substrate or microchip 58 (see also FIG. 2). Each of the sensors50, 54 includes an array of individual (e.g., four or more) Hall sensingelements arranged in a line. Particularly, in one embodiment of theencoder 10, each of the sensors 50, 54 may include an array of sixteenindividual Hall sensing elements arranged in a line. With reference toFIG. 1, both the reference sensor 54 and the high-resolution sensor 50have a length sufficient to span adjacent pole junctions 30 in themagnetic track 14 and detect the presence of adjacent pole junctions 30at any given time (i.e., at least one North/South pole junction 30 andat least one adjacent South/North pole junction 30). In other words, thelength of each of the sensors 50, 54 is greater than the spacing betweenadjacent pole junctions. The amount of offset between thehigh-resolution segment 34 and the reference segment 42 a or 42 b ineach pole junction 30 may be less than the spacing between adjacentindividual Hall sensing elements in the reference sensor 54.Alternatively, the high-resolution sensor 50 may not span adjacent polejunctions 30 in the magnetic track 14. As a further alternative, thesensors 50, 54 may be disposed on separate microchips, or the individualsensor elements in each sensor array may be independently supported fromeach other as distinct Hall-effect sensors.

With reference to FIGS. 1 and 2, the magnetic encoder 10 also includes alogic module 62 in communication with the sensors 50, 54. The logicmodule 62 may be a hard-wired electronic circuit or a microprocessoroperable to receive high-resolution and reference signals detected bythe sensors 50, 54, respectively, analyze the signals, and calculate thelocal absolute position of the magnetic track 14 within the group 26 offour pole pairs 18 a-18 d. The logic module 62 may be positioned on themicrochip 58 with the sensors 50, 54, or the logic module 62 may bepositioned on another substrate besides the microchip 58. Although aphysical (i.e., wired) connection is schematically illustrated in FIGS.1 and 2, wireless communication may be employed to allow the sensors 50,54 to communicate with the logic module 62. The logic module 62 isfurther operable to output the local absolute position of the magnetictrack 14 within the group 26 of four pole pairs 18 a-18 d to anothercontroller (e.g., a motor controller) in the system in which the encoder10 is used.

As understood by those skilled in the art, the high-resolution sensor 50can be configured with a particular resolution (i.e., “counts” or“edges” per pole pair) to yield a total number of counts or edges perrevolution of the magnetic track 14. For example, thehigh-resolutionsensor 50 may be configured having a resolution of 160 counts/pole pair,such that a total of 640 counts may be detected as the magnetic track 14rotates through the group 26 of four pole pairs 18 a-18 d shown inFIG. 1. To arrive at the 640 count total, the high-resolution sensor 50would count from 1 to 160 for the first pole pair 18 a (with counts 1-80occurring within the North pole and counts 81-160 occurring within theSouth pole of the first pole pair 18 a), reset, and continue countingfrom 1 to 160 for the second pole pair 18 b and so forth.

However, as previously mentioned, only a portion of the magnetic track14 is shown in FIG. 1. A typical application of the encoder 10 mightrequire at least 16 magnetic pole pairs on the magnetic track 14. Inthis situation, the group 26 of four pole pairs 18 a-18 d shown in FIG.1 would be repeated four times around the circumferential length of themagnetic track 14 to yield the requisite 16 pole pairs. As such, theabsolute position of the magnetic track 14 may be determined locallywithin a quarter-turn of the rotating target 22 to which the magnetictrack 14 is attached using the unique combination of adjacentright-offset and left-offset reference segments 42 a, 42 b shown in FIG.1 and described in Table 1.

During operation of the encoder 10 (i.e., when the rotating target 22and magnetic track 14 are rotating relative to the sensors 50, 54 in aclockwise or left-to-right direction from the perspective of FIG. 1),the high-resolution sensor 50 is configured to detect the magnetic fieldemanated by the high-resolution portion 38 of the track 14, and thereference sensor 54 is configured to detect the magnetic field emanatedby the reference portion 46 of the track 14. The analog output of eachof the sensors 50, 54 is sinusoidal, having a positive value associatedwith the North pole in each pole pair 18 a-18 d and a negative valueassociated with the South pole in each pole pair 18 a-18 d. As a resultof the unequal spacing of the reference segments 42 a, 42 b of the polejunctions 30, the sinusoidal output of the reference sensor 54 is out ofphase with the sinusoidal output of the high-resolution sensor 50.

The sinusoidal output of each of the sensors 50, 54 is input to thelogic module 62, which compares the sinusoidal output of each of thesensors 50, 54 and determines whether the phase of the sinusoidal outputof the reference sensor 54 is leading the sinusoidal output of thehigh-resolution sensor or lagging the sinusoidal output of thehigh-resolution sensor 50. More particularly, the logic module 62 maycompare the sinusoidal output of the individual Hall elements of thereference sensor 54, respectively, with the sinusoidal output of theindividual Hall elements of the high-resolution sensor 50.Alternatively, the logic module 62 may compare a rolling average of theoutput of a group (e.g., three or six) of adjacent Hall elements of thereference sensor 54, respectively, with the rolling average of theoutput of a group of adjacent Hall elements of the high-resolutionsensor 50.

In other words, the logic module 62 is operable to determine whether thereference sensor 54 is disposed proximate a left-offset referencesegment 42 b (i.e., when the sinusoidal output of the reference sensor54 is leading the sinusoidal output of the high-resolution sensor 50),or whether the reference sensor 54 is disposed proximate a right-offsetreference segment 42 a (i.e., when the sinusoidal output of thereference sensor 54 is lagging the sinusoidal output of thehigh-resolution sensor 50). Since the reference sensor 54 spans thedistance between at least one North/South pole junction 30 and at leastone South/North pole junction 30 on the magnetic track 14, the referencesensor 54 is operable to detect adjacent North/South and South/Northpole junctions 30, and the logic module 62 is operable to correlate theparticular combination of North/South and South/North pole junctions 30detected by the reference sensor 54 with one of the magnetic pole pairs18 a-18 d in the group 26 of four pole pairs 18 a-18 d shown in FIG. 1to determine a relative position of the particular pole pair 18 a-18 dwithin the group 26. It should be understood that the encoder 10 isoperable in this manner when the magnetic track 14 is rotating relativeto the reference sensor 54 or stationary.

With continued reference to FIG. 1, the magnetic track 14 is shownrotated to a position in which the reference sensor 54 spans theNorth/South pole junction 30 of the third pole pair 18 c and theSouth/North pole junction 30 between the third and fourth pole pairs 18c, 18 d, respectively. In this instance, the logic module 62 would beable to determine the absolute position of the magnetic track 14 locallywithin the group 26 of four pole pairs 18 a-18 d by recognizing theright-offset reference segment 42 a associated with the North/South polejunction 30 of the third pole pair 18 c and the left-offset referencesegment 42 b associated with the South/North pole junction 30 betweenthe third and fourth pole pairs 18 c, 18 d, respectively, by comparingthe phase difference of the sinusoidal outputs of the reference sensor54 and the high-resolution sensor 50 as described above. Then, the logicmodule 62 would reference a lookup table similar to Table 1 to find thatonly the third pole pair 18 c includes the detected combination ofright-offset and left-offset reference segments 42 a, 42 b, meaning thattwo pairs (i.e., pole pairs 18 a and 18 b) are to the left of thereference sensor 54 and the reference sensor 54 is proximate or alignedwith the third pole pair 18 c. The logic module 62 may then calculatethe local absolute position within the group 26 using the recorded orcaptured count value of the high-resolution sensor 50 and the relativeposition of the third pole pair 18 c within the group 26. Specifically,the logic module 62 would perform the following calculation to determinethe local absolute position of the magnetic track 14 within the group 26of four pole pairs 18 a-18 d: 2 pole pairs to the left of the referencesensor 54×160 counts/pole pair+the number of counts detected or capturedby the high-resolution sensor 50. For example, at an instance when thecaptured count value of the high-resolution sensor 50 is 70, thecalculated count value would be equal to 390 (i.e., 2×160+70), whichcorrelates to the 390^(th) position of the 640 total count positionsthat can be detected by the sensor 50 within the local group 26 of fourmagnetic pole pairs 18 a-18 d.

Considering another example, with reference to FIG. 3, the magnetictrack 14 is shown rotated to a position in which the reference sensor 54spans the South/North pole junction 30 between the first pole pair 18 aand the second pole pair 18 b and the North/South pole junction 30within the second pole pair 18 b. In this instance, the logic module 62would be able to determine the absolute position of the magnetic track14 within the local group 26 of four pole pairs 18 a-18 d by recognizingthe left-offset reference segment 42 b associated with the South/Northpole junction 30 between the first and second pole pairs 18 a, 18 b andthe left-offset reference segment 42 b associated with the North/Southpole junction 30 within the second pole pair 18 b by comparing the phasedifference of the sinusoidal outputs of the reference sensor 54 and thehigh-resolution sensor 50 as described above. Then, the logic module 62would reference a lookup table similar to Table 1 to find that thedetected combination of right-offset and left-offset reference segments42 a, 42 b places the reference sensor 54 somewhere between the firstand second pole pairs 18 a, 18 b.

The logic module 62 would then look to the count value captured by thehigh-resolution sensor 50. If the captured count value is between 81 and160, then the local absolute position is somewhere within the first polepair 18 a. However, if the captured count value is between 1 and 80,then the local absolute position is somewhere within the second polepair 18 b. For a count value of the high-resolution sensor 50 equal to30, the logic module 62 would perform the following calculation todetermine the absolute position within the local group 26 of four polepairs 18 a-18 d: 1 pole pair to the left of the reference sensor 54×160counts/pole pair+30=190, which correlates to the 190^(th) position ofthe 640 total counts that can be detected by the sensor 50 within thelocal group 26 of four magnetic pole pairs 18 a-18 d. For a count valueof the high-resolution sensor 50 equal to 130, the logic module 62 wouldperform the following calculation to determine the absolute positionwithin the local group 26 of four pole pairs 18 a-18 d: 0 pole pairs tothe left of the reference sensor 54×160 counts/pole pair+130=130, whichcorrelates to the 130^(th) position of the 640 total count positionsthat can be detected by the sensor 50 within the local group 26 of fourmagnetic pole pairs 18 a-18 d.

With reference to FIG. 4, conventional magnetic encoders E typicallyinclude three separate Hall-effect sensors U, V, W, a dedicated magnetictrack T1 having one or more North/South pole pairs (only a singleNorth/South pole pair is shown in FIG. 4), and a high-resolutionmagnetic track T2 attached to a common rotating target (e.g., anarmature of an electric motor). The sensors U, V, W are spaced about therotational axis of the tracks T1, T2 at 120 degree intervals, and areswitched “on” and “off” by detecting the pole junctions between theindividual pole pairs of the track T1. As such, each sensor U, V, W isturned “on” for 180 degrees of rotation of the magnetic track T1, andeach sensor U, V, W is turned “off” for 180 degrees of rotation of themagnetic track T1 (see FIG. 5). As a result, the position of themagnetic tracks T1, T2 may be determined using the unique combinationsof “on” and “off” states of the sensors U, V, W over a single completerevolution of the magnetic tracks T1, T2 and the associated rotatingtarget. For example, Table 2 below illustrates six different rotationalpositions of the magnetic track T1 and the associated rotating targetbased upon the unique combinations of “on” and “off” states exhibited bythe sensors U, V, W:

TABLE 2 Rotational Rotational Position U, V, W Output Position No.(degrees) (1 = “on”; 0 = “off”) 1  0-60 1, 0, 1 2  61-120 1, 0, 0 3121-180 1, 1, 0 4 181-240 0, 1, 0 5 241-300 0, 1, 1 6 301-360 0, 0, 1

Using the U, V, W commutation signals output by the magnetic encoder Eof FIG. 4, a controller interfacing with the magnetic encoder E maydetermine the rotational position of the tracks T1, T2 and theassociated rotating target (i.e., within 60 degree increments). Forexample, the magnetic encoder E shown in FIG. 4 may be implemented witha motor controller for detecting the position of an armature of abrushless DC electric motor with respect to the field component of themotor at a frequency of four times per revolution of the armature. So,once per quarter-turn of the armature, the U, V, W output of themagnetic encoder E is analyzed by the motor controller to determine therelative position of the armature and the tracks T1, T2 with respect tothe field component of the motor (i.e., the U, V, W output willcorrelate to one of Positions 1-6; see Table 2). The motor controllerthen uses this information to switch the current direction through thearmature to cause the armature to rotate continuously with respect tothe field component of the motor.

The encoder 10 of FIG. 1 may be used to create the same U, V, Wcommutation signals without the additional Hall-effect sensors U, V, Wand the dedicated, single pole-pair magnetic track T1. Specifically, inan application of the encoder 10 requiring 16 pole pairs in the magnetictrack 14, the group 26 of four pole pairs 18 a-18 d shown in FIG. 1would be repeated four times around the circumferential length of themagnetic track 14 to yield the requisite 16 pole pairs, such that eachgroup 26 coincides with a quarter-turn or 90 degrees of rotation of themagnetic track 14 and the rotating target 22. The logic module 62,therefore, is capable of creating a square wave similar to the “U”output of FIG. 5 having a value of “1” for two consecutive pole pairgroups 26 and a value of “0” for the following two consecutive pole pairgroups 26. The logic module 62 may then create a second square wavesimilar to the “V” output of FIG. 5 that is out of phase with the Uoutput by 120 degrees, and a third square wave similar to the “W” outputof FIG. 5 that is out of phase with the U output by 240 degrees. Usingthe brushless DC electric motor example above, the square waves createdby the logic module 62 may be input to the motor controller which, in asimilar manner as described above, would use this information to switchthe current direction through the armature to cause the armature torotate continuously with respect to the field component of the motor.

The encoder 10 may also be used to determine the absolute position ofthe magnetic track 14 and the attached rotating target 22 over acomplete revolution if the single group 26 of pole pairs 18 a-18 d spansa complete revolution of the rotating target 22. In this situation, thecalculated count position is not only indicative of the local absoluteposition within the group 26 of four pole pairs 18 a-18 d, but also isindicative of the absolute position of the magnetic track 14 over acomplete revolution of the rotating target 22. The encoder 10 may alsoreplace a resolver in some brushless DC/AC electric motor applications.

With reference to FIG. 6, another embodiment of a sensor assembly ormagnetic encoder 66 is schematically illustrated, with like componentshaving like reference numerals. The encoder 66 includes a magnetic track70, attached to a rotating target 74, having five of the groups 26 ofpole pairs 18 a-18 d shown in FIG. 1 positioned end to end andcircularly arranged. The encoder 66 also includes a high-resolutionsensor 50 and a reference sensor 54 on a single microchip 58, and alogic module 62 in communication with the sensors 50, 54. The encoder 66further includes a dedicated, single pole-pair magnetic track 78attached to the rotating target 74 and three Hall-effect sensors 82 a-82c spaced about the rotational axis of the tracks 70, 78 at 120-degreeintervals. Each of the sensors 82 a-82 c is switched “on” and “off” bydetecting the pole junctions between the individual pole pairs of thetrack 70. As such, each sensor 82 a-82 c is turned “on” for 180 degreesof rotation of the magnetic track 70, and each sensor 82 a-82 c isturned “off” for 180 degrees of rotation of the magnetic track 70,thereby outputting signals similar to the commutation signals shown inFIG. 5. As such, the three Hall-effect sensors 82 a-82 c are capable ofdetermining six different windows or rotational positions each includinga portion of the magnetic track 70.

In operation of the encoder 66, the output of the separate Hall-effectsensors 82 a-82 c, the high-resolution sensor 50, and the referencesensor 54 may be utilized to determine the absolute position of themagnetic track 70 over a complete revolution of the rotating target 74(i.e., the “full-on” absolute position). The magnetic track 70 includesa resolution or a total number of count positions equal to 3200 (i.e., 5groups×4 pole pairs/group×160 counts/pole pair) as a result of stringingtogether the five pole pair groups 26. At a given instance, the logicmodule 62 records or captures a relative count position or count valueon the high-resolution portion of the magnetic track 70 using thehigh-resolution sensor 50. Then, the captured count value is used tocalculate the absolute position within one of the local pole pair groups26 using the process described above. At the same time the count valueusing the high-resolution sensor 50 is captured, the logic module 62captures the particular logic state of the Hall-effect sensors 82 a-82 c(i.e., the logic state corresponding with one of Positions 1-6 in Table2). Then, the logic module 62 may correlate the captured position numberor window with the particular pole pair group 26 that contains thecaptured count value by the high-resolution sensor 50 to determine arelative position of the particular pole pair group 26 within themagnetic track 70. Knowing which of the five groups 26 contains thecaptured count value by the high-resolution sensor 50, the logic module62 may then calculate the absolute position number on the magnetic track70 using the calculated local absolute position within the particularpole pair group 26 and the relative position of the particular group 26within the magnetic track 70. For example, if the logic module 62calculates the local absolute position of the track 70 is equal to 400(of the 640 total count positions in each group 26), and the logicmodule 62 has correlated the detected position number (i.e., one ofPositions 1-6) with the fourth group 26 of pole pairs, then the absoluteposition of the magnetic track 70 may be calculated as: 3 groups to theleft of the reference sensor 54×640 counts/group+400 counts=2320, whichis one of the 3200 total count positions on the magnetic track 70.

With reference to FIG. 7, yet another embodiment of a sensor assembly ora magnetic encoder 86 is schematically illustrated, with like componentshaving like reference numerals. The encoder 86 includes a magnetic track90 having a plurality of North/South pole pairs 94 a-94 i. Although themagnetic track 90 is schematically illustrated in a linear configurationfor clarity, the encoder 86 is configured as a rotary encoder includinga rotating target 98 upon which the magnetic track 90 is mounted. Insuch a configuration, the magnetic track 90 would be circular andconcentric with the rotational axis of the rotating target 98. However,the encoder 86 of the present invention may alternatively be configuredas a linear encoder, incorporating substantially similar structure and amethod of operation as described herein with respect to the rotaryencoder 86.

With continued reference to FIG. 7, only a portion of the magnetic track90 is shown. Specifically, the illustrated portion of the magnetic track90 includes a group 100 of nine pole pairs 94 a-94 i, each of whichincludes a pole junction 102 separating the individual North/South polesin the respective pole pairs 94 a-94 i. Each of the pole junctions 102is divided into a high-resolution segment 106 corresponding with ahigh-resolution portion 110 of the magnetic track 90, and a referencesegment 114 a-114 c corresponding with a reference portion 118 of themagnetic track 90. However, unlike the magnetic track 14 illustrated inFIG. 1, some of the pole junctions 102 in the magnetic track 90 arestraight, such that the reference segment 114 a in each of the straightpole junctions 102 is aligned with the high-resolution segment 106 ofthe same pole junction 102, while other pole junctions 102 in themagnetic track 90 are jogged or stepped, such that the reference segment114 b, 114 c in each of the jogged pole junctions 102 is offset from thehigh-resolution segment 106 of the same pole junction 102. Thehigh-resolution segments 106 of adjacent pole junctions 102 are equallyspaced from each other, while the reference segments 114 a-114 c ofadjacent pole junctions 102 may be unequally spaced, depending upon thedirection of offset (or lack of offset) of the adjacent referencesegments 114 a-114 c.

With reference to FIG. 7, some of the pole junctions 102 include areference segment 114 b that is offset to the right of thehigh-resolution segment 106 of the same pole junction 102 (i.e., aright-offset reference segment 114 b), some pole junctions 102 include areference segment 114 c that is offset to the left of thehigh-resolution segment 106 of the same pole junction 102 (i.e., aleft-offset reference segment 114 c), while other pole junctions 102 arestraight and include a reference segment 114 a that is aligned with thehigh-resolution segment 106 of the same pole junction 102 (i.e., azero-offset reference segment 114 a). The reference segments 114 a-114 cmay be arranged within the group 100 of adjacent magnetic pole pairs 94a-94 i to provide a unique combination or sequence of states (e.g.,either right-offset, left-offset, or zero-offset) for each pole pair 94a-94 i in the group 100. As a result, a particular pole pair 94 a-94 imay be identified by matching it with its associated unique combinationof adjacent reference segments 114 a-114 c. Using this “three-state”logic (i.e., using zero-offset, right-offset, and left-offset referencesegments 114 a-114 c), the nine adjacent pole pairs 94 a-94 iillustrated in FIG. 7 can be uniquely identified according to Table 3below, in which “0” denotes a zero-offset reference segment 114 a, “R”denotes a right-offset reference segment 114 b, and “L” denotes aleft-offset reference segment 114 c.

TABLE 3 Pole Pole Pairs Junctions 1 2 3 4 5 6 7 8 9 North/South 0 0 0 LL L R R R South/North 0 L R 0 L R 0 L RThe North/South pole junction is the pole junction 102 between the Northand South poles within a particular pole pair 94 a-94 i, while theSouth/North pole junction is the pole junction 102 between the Southpole and the North pole of adjacent pole pairs 94 a-94 i. As describedin more detail below, the magnetic encoder 86 is operable to determinethe absolute position of the magnetic track 90 locally within the group100 of nine magnetic pole pairs 94 a-94 i by recognizing the uniquecombination of adjacent zero-offset, right-offset, and left-offsetreference segments 114 a-114 c separating the individual poles in thepole pairs 94 a-94 i.

With continued reference to FIG. 7, the magnetic encoder 86 alsoincludes a first or high-resolution magnetic sensor 50 proximate thehigh-resolution portion 110 of the track 90, a second magnetic sensor 54proximate the reference portion 118 of the track 90, and a logic module62 in communication with the sensors 50, 54. As discussed in more detailbelow, the logic module 62 is operable to receive high-resolution andreference signals detected by the sensors 50, 54, respectively, analyzethe signals, and calculate the local absolute position of the magnetictrack 90 within the group 100 of nine pole pairs 94 a-94 i, andtherefore the local absolute position of the rotating target 98, toanother controller (e.g., a motor controller) in the system in which theencoder 86 is used.

As understood by those skilled in the art, the high-resolution sensor 50can be configured with a particular resolution (i.e., “counts” or“edges” per pole pair) to yield a total number of counts or edges perrevolution of the magnetic track 90. For example, the high-resolutionsensor 50 may be configured having a resolution of 160 counts/pole pair,such that a total of 1440 counts may be detected as the magnetic track90 rotates through the group 100 of nine pole pairs 94 a-94 i shown inFIG. 7. However, as previously mentioned, only a portion of the magnetictrack 90 is shown in FIG. 7. A typical application of the encoder 86might require more than nine pole pairs 94 a-94 i on the magnetic track90. In this situation, the group 100 of nine pole pairs 94 a-94 i shownin FIG. 7 would be repeated two or more times around the circumferentiallength of the magnetic track 90 to yield the requisite number of polepairs. As such, the absolute position of the magnetic track 90 may bedetermined locally within a fractional turn of the rotating target 98 towhich the magnetic track 90 is attached (i.e., a half-turn, a one-thirdturn, a quarter-turn, etc.) using the unique combination of adjacentzero-offset, right-offset, and left-offset reference segments 114 a-114c shown in FIG. 7 and described in Table 3.

During operation of the encoder 86, the generally sinusoidal output ofeach of the sensors 50, 54 is input to the logic module 62, whichcompares the sinusoidal output of each of the sensors 50, 54 anddetermines whether the phase of the sinusoidal output of the referencesensor 54 is leading the sinusoidal output of the high-resolution sensor50, lagging the sinusoidal output of the high-resolution sensor 50, orin phase with the sinusoidal output of the high-resolution sensor 50.The logic module 62 may compare the sinusoidal output of the individualHall elements of the reference sensor 54, respectively, with thesinusoidal output of the individual Hall elements of the high-resolutionsensor 50. Alternatively, the logic module 62 may compare an analog ordigital a rolling average of the output of a group (e.g., four) of Hallelements of the reference sensor 54, respectively, with the rollingaverage of the output of a group of Hall elements of the high-resolutionsensor 50. The groups of Hall elements in each of the sensors 50, 54 mayinclude consecutive or adjacent Hall elements in each of the sensors 50,54. Alternatively, the groups of Hall elements in each of the sensors50, 54 may include non-consecutive or non-adjacent Hall elements in eachof the sensors 50, 54.

In other words, the logic module 62 is operable to determine whether thereference sensor 54 is disposed proximate a left-offset referencesegment 114 c (i.e., when the sinusoidal output of the reference sensor54 is leading the sinusoidal output of the high-resolution sensor 50),whether the reference sensor 54 is disposed proximate a right-offsetreference segment 114 b (i.e., when the sinusoidal output of thereference sensor 54 is lagging the sinusoidal output of thehigh-resolution sensor 50), or whether the reference sensor 54 isdisposed proximate a zero-offset reference segment 114 a (i.e., when thesinusoidal output of the reference sensor 54 is in phase with thesinusoidal output of the high-resolution sensor 50). Since the referencesensor 54 spans the distance between at least one North/South polejunction 102 and at least one adjacent South/North pole junction 102 onthe magnetic track 90, the logic module 62 is operable to correlate theparticular combination of North/South and South/North pole junctions 102detected by the reference sensor 54 with one of the magnetic pole pairs94 a-94 i in the group 100 of nine pole pairs 94 a-94 i shown in FIG. 7.It should be understood that the encoder 86 is operable in this mannerwhen the magnetic track 90 is rotating relative to the reference sensor54 or stationary.

With continued reference to FIG. 7, the magnetic track 90 is shownrotated to a position in which the reference sensor 54 spans theNorth/South pole junction 102 of the fifth pole pair 94 e and theSouth/North pole junction 102 between the fifth and sixth pole pairs 94e, 94 f. In this instance, the logic module 62 would be able todetermine the absolute position of the magnetic track 90 locally withinthe group 100 of nine pole pairs 94 a-94 i by recognizing theleft-offset reference segment 114 c associated with the North/South polejunction 102 of the fifth pole pair 94 e and the left-offset referencesegment 114 c associated with the South/North pole junction 102 betweenthe fifth and sixth pole pairs 94 e, 94 f by comparing the phasedifference of the sinusoidal outputs of the reference sensor 54 and thehigh-resolution sensor 50 as described above. Then, the logic module 62would reference a lookup table similar to Table 3 to find that only thefifth pole pair 94 e includes the detected combination of left-offsetand left-offset reference segments 114 c, meaning that four completepole pairs (i.e., pole pairs 94 a-94 d) are to the left of the referencesensor 54 and the reference sensor 54 is proximate or aligned with thefifth pole pair 94 e. The logic module 62 would then perform thefollowing calculation to determine the local absolute position of themagnetic track 90 within the group 100 of nine pole pairs 94 a-94 i: 4pole pairs to the left of the reference sensor 54×160 counts/polepair+the number of counts detected by the high-resolution sensor 50. Forexample, at an instance when the captured count value of thehigh-resolution sensor 50 is 70, the calculated count value would beequal to 710 (i.e., 4×160+70), which correlates to the 710^(th) positionof the 1440 total count positions that can be detected by the sensor 50within the local group 100 of nine magnetic pole pairs 94 a-94 i.

Considering another example, with reference to FIG. 8, the magnetictrack 90 is shown rotated to a position in which the reference sensor 54spans the South/North pole junction 102 between the seventh pole pair 94g and the eighth pole pair 94 h and the North/South pole junction 102within the eighth pole pair 94 h. In this instance, the logic module 62would be able to determine the absolute position of the magnetic track90 within the local group 100 of nine pole pairs 94 a-94 i byrecognizing the zero-offset reference segment 114 a associated with theSouth/North pole junction 102 between the seventh and eighth pole pairs94 g, 94 h and the right-offset reference segment 114 b associated withthe North/South pole junction 102 within the eighth pole pair 94 h bycomparing the phase difference of the sinusoidal outputs of thereference sensor 54 and the high-resolution sensor 50 as describedabove. Then, the logic module 62 would reference a lookup table similarto Table 3 to find that the detected combination of zero-offset andright-offset reference segments 114 a, 114 b places the reference sensor54 somewhere between the seventh and eighth pole pairs 94 g, 94 h. Thelogic module 62 would then look to the count value captured by thehigh-resolution sensor 50. If the captured count value is between 81 and160, then the local absolute position is somewhere within the seventhpole pair 94 g. However, if the captured count value is between 1 and80, then the local absolute position is somewhere within the eighth polepair 94 h. For a captured count value of the high-resolution sensor 50equal to 30, the logic module 62 would perform the following calculationto determine the absolute position within the local group 100 of ninepole pairs 94 a-94 i: 7 pole pairs to the left of the reference sensor54×160 counts/pole pair+30=1150, which correlates to the 1150^(th)position of the 1440 total count positions that can be detected by thesensor 50 within the local group 100 of nine magnetic pole pairs 94 a-94i. For a captured count value of the high-resolution sensor 50 equal to130, the logic module 62 would perform the following calculation todetermine the absolute position within the local group 100 of nine polepairs 94 a-94 i: 6 pole pairs to the left of the reference sensor 54×160counts/pole pair+130=1090, which correlates to the 1090^(th) position ofthe 1440 total count positions that can be detected by the sensor 50within the local group 100 of nine magnetic pole pairs 94 a-94 i.

The encoder 86 of FIG. 7 may be used to create U, V, W commutationsignals in a similar manner as the encoder 10 of FIG. 1. The encoder 86may also be used to determine the absolute position of the magnetictrack 90 over a complete revolution of the rotating target 98 if thesingle group 100 of nine pole pairs 94 a-94 i spans a completerevolution of the rotating target 98. In this situation, the calculatedcount position is not only indicative of the local absolute positionwithin the group 100 of nine pole pairs 94 a-94 i, but also isindicative of the absolute position of the magnetic track 90 over acomplete revolution of the rotating target 98.

Alternatively, the encoder 86 may include a magnetic track (not shown),attached to a rotating target, having five of the groups 100 of polepairs 94 a-94 i shown in FIG. 7 positioned end to end and circularlyarranged. The encoder 86 may also include a dedicated, single pole-pairmagnetic track attached to the rotating target and three Hall-effectsensors spaced about the rotational axis of the tracks at 120 degreeintervals in a similar manner to the encoder 66 of FIG. 6. The output ofthe separate Hall-effect sensors, the high-resolution sensor 50, and thereference sensor 54 may be utilized to determine the absolute positionof the magnetic track over a complete revolution of the rotating targetin a similar manner as the encoder 66 of FIG. 6. The magnetic trackwould include a resolution or a total number of count positions equal to7200 (i.e., 5 groups×9 pole pairs/group×160 counts/pole pair) as aresult of stringing together the five pole pair groups 100.

With reference to FIG. 9, another embodiment of a sensor assembly ormagnetic encoder 122 of the present invention can be configured using“four-state” logic, thereby increasing the number of pole pairs in eachgroup to sixteen, such that additional Hall-effect sensors (e.g.,sensors 82 a-82 c in FIG. 6) and a separate single pole-pair magnetictrack 78 (e.g., track in FIG. 6) are not required to determine theabsolute position of a magnetic track having a total of sixteen polepairs. FIG. 9 illustrates a portion of a magnetic track 126 of theencoder 122, including right-offset reference segments 130 that arespaced from a high-resolution segment 134 in the same pole junction 138by a dimension D, and right-offset reference segments 142 that arespaced from the high-resolution segment 134 in the same pole junction138 by a dimension D/2. In a similar manner, the track 126 includesleft-offset reference segments 146 that are spaced from thehigh-resolution segment 134 in the same pole junction 138 by a dimensionD, and left-offset reference segments 150 that are spaced from thehigh-resolution segment 134 in the same pole junction 138 by a dimensionD/2. The logic module 62 may be configured, therefore, to recognize thedifference between the reference segments 130, 142, 146, 150 having theD and D/2 spacing to increase the number of pole pairs in the localgroup from nine to 25. The encoder 122 could alternatively be configuredusing “five-state” logic by incorporating a straight pole junction inaddition to the illustrated offset pole junctions shown in FIG. 9,thereby increasing the number of pole pairs in each group totwenty-five.

Various features of the invention are set forth in the following claims.

What is claimed is:
 1. A method of determining a position on a magnetictrack of an encoder, the method comprising: providing a group ofmagnetic pole pairs that forms a portion of the magnetic track;recording a relative position within a first magnetic pole pair in thegroup using a first magnetic sensor proximate a high-resolution portionof the magnetic track; detecting adjacent pole junctions within thegroup of magnetic pole pairs with a second magnetic sensor positionedproximate a reference portion of the magnetic track; correlating theadjacent pole junctions with the first magnetic pole pair to determine arelative position of the first magnetic pole pair within the group; andcalculating a local absolute position within the group using therelative position within the first magnetic pole pair and the relativeposition of the first magnetic pole pair within the group.
 2. The methodof claim 1, wherein the group of magnetic pole pairs is a first group,and wherein the method further includes arranging a plurality of polepair groups identical to the first group end to end with the firstgroup.
 3. The method of claim 2, wherein the magnetic track is a firstmagnetic track, and wherein the method further comprises: providing asecond magnetic track including a single magnetic pole pair and two polejunctions; detecting the pole junctions using a plurality of Hall-effectsensors substantially equally spaced from each other and positionedproximate the second magnetic track; and creating a plurality of windowsusing the output of the Hall-effect sensors, wherein each windowincludes a portion of the magnetic track.
 4. The method of claim 3,further comprising: correlating the first group of magnetic pole pairswith one of the windows to determine a relative position of the firstgroup within the first magnetic track; and calculating an absoluteposition on the first magnetic track using the calculated local absoluteposition within the first group and the relative position of the firstgroup within the first magnetic track.
 5. The method of claim 2, whereineach pole pair group includes four magnetic pole pairs, and whereinconsecutive pairs of adjacent pole junctions in the group are differentfrom each other.
 6. The method of claim 2, wherein each pole pair groupincludes nine magnetic pole pairs, and wherein consecutive pairs ofadjacent pole junctions in the group are different from each other. 7.The method of claim 2, wherein each pole pair group includes at leastfour magnetic pole pairs, and wherein consecutive pairs of adjacent polejunctions in the group are different from each other.
 8. The method ofclaim 1, wherein the first magnetic sensor and/or the second magneticsensor is a Hall string multiplying sensor supported on a microchip. 9.The method of claim 8, wherein the first and second magnetic sensors areconfigured as Hall string multiplying sensors supported on the samemicrochip.
 10. The method of claim 1, wherein each of the first andsecond magnetic sensors includes an array of at least 4 Hall sensingelements.
 11. The method of claim 1, wherein each of the adjacent polejunctions includes a high-resolution segment corresponding with thehigh-resolution portion of the magnetic track and a reference segmentcorresponding with the reference portion of the magnetic track, andwherein the reference segment of each pole junction is offset or alignedwith the corresponding high-resolution segment in each pole junction.12. The method of claim 11, wherein the reference segment of one of theadjacent pole junctions is offset from the high-resolution segment ofthe same pole junction in a first direction.
 13. The method of claim 12,wherein the reference segment of the other of the adjacent polejunctions is offset from the high-resolution segment of the same polejunction in the first direction.
 14. The method of claim 12, wherein thereference segment of the other of the adjacent pole junctions is offsetfrom the high-resolution segment of the same pole junction in a seconddirection opposite the first direction.
 15. The method of claim 12,wherein the reference segment of the other of the adjacent polejunctions is aligned with the high-resolution segment of the same polejunction.
 16. The method of claim 11, wherein the reference segment ofone of the adjacent pole junctions is offset from the high-resolutionsegment of the same pole junction in a first direction by a firstamount, and wherein the reference segment of the other of the adjacentpole junctions is offset from the high-resolution segment of the samepole junction in the first direction by a second amount different thanthe first amount.
 17. The method of claim 11, wherein the plurality ofmagnetic poles and pole junctions define at least four magnetic polepairs, and wherein the reference segment of each pole junction on themagnetic track is offset from the high-resolution segment of the samepole junction.
 18. The method of claim 11, wherein the plurality ofmagnetic poles and pole junctions define at least nine magnetic polepairs, wherein the reference segment of at least one pole junction onthe magnetic track is offset from the high-resolution segment of thesame pole junction in a first direction, wherein the reference segmentof at least one pole junction on the magnetic track is offset from thehigh-resolution segment of the same pole junction in a second directionopposite the first direction, and wherein the reference segment of atleast one pole junction on the magnetic track is aligned with thehigh-resolution segment of the same pole junction.
 19. The method ofclaim 1, wherein the step of detecting adjacent pole junctions withinthe group of magnetic pole pairs with the second magnetic sensor occurswhen the magnetic track is rotating relative to the second magneticsensor.
 20. The method of claim 1, wherein the step of detectingadjacent pole junctions within the group of magnetic pole pairs with thesecond magnetic sensor occurs when the magnetic track is stationaryrelative to the second magnetic sensor.